A CVD process is widely used for forming an insulating film such as a silicon oxide film, a high dielectric constant insulating film or the like in a manufacturing process for various kinds of semiconductor devices. The CVD process forms the insulating film on an object to be processed by vaporizing a raw material using an energy such as heat and the like.
The following problems have been noted when forming an insulating film using the CVD process. The first problem is that an interface-level density becomes higher because microscopic asperity portions are formed on the interface between the insulating film and an underlying layer deposited by the CVD process. If the interface-level density becomes higher, for example, there is concern that the mobility of carriers moving at the interface between the silicon layer and the insulating film becomes lower and electrical performance of a device is deteriorated when the underlying layer is a silicon layer. Also, since the film thickness varies according to the asperity portions, there exist microscopically weak portions, thereby affecting the lifetime of insulation breakdown.
Also, the second problem is that an insulating film (e.g. a silicon oxide film) formed using a CVD process or a plasma CVD process does not have a good film quality, because the insulating film includes many dangling bonds and impurities such as moisture, chlorine or the like derived from the raw material. As a result, the film quality is needed to be improved by annealing the insulating film formed by the CVD process or the plasma CVD process at a high temperature, for example, of above 700° C. But, it is hard to improve the fundamental film quality by the annealing process after forming the film, because it is impossible to recombine Si—O bonds by supplying thermal energy. Also, although processing at a high temperature is necessary to improve the modification effect, an annealing process at a high temperature requires an increased thermal budget, making it hard to control the distribution of impurities dispersed in a silicon layer, and accordingly giving an undesirable effect to the quality of semiconductor devices.
Also, for example, when using a synthetic resin substrate or a glass substrate such as in the liquid crystal display or organic electroluminescent display, it is impossible to perform the annealing process at a high temperature for modifying an insulating film.
Accordingly, a technique has been proposed for modifying the film quality at a relatively low temperature by processing a silicon oxide film with plasma. See, for example, WO 2002/059956 and WO 2001/69665.